Spray 3 1/2- to 4-quart slow cooker with cooking spray. In 12-inch nonstick skillet, cook beef, onion and garlic over medium- high heat 5 to 7 minutes, stirring occasionally, until beef is thoroughly cooked; drain.
Spoon 3/4 cup of the pasta sauce in bottom of slow cooker. Layer half of the ravioli, half of the beef mixture and 1 cup of the cheese over sauce. Repeat layers with 3/4 cup sauce, remaining ravioli and remaining beef mixture. Top with remaining sauce; sprinkle with remaining 1 cup cheese.
Cover; cook on Low heat setting 6 hours or until ravioli is tender.